In the past several years, a new technology, called the DNA array, has attracted interest among biologists. This technology promises to monitor part or all of an organism's genome on a single chip so that researchers can develop a better picture of the interactions among hundreds or thousands of genes simultaneously. This technology has been termed biochip, DNA chip, DNA microarray, gene array, and genome chip. Generally, a DNA array relies upon standard base pairing rules developed by Watson and Crick to analyze the presence, or the sequence, of a particular complementary nucleic acid sequence.
More recently, attention has focused on fabrication of protein or peptide arrays, and this area is commonly referred to as “proteomics.” In one example of this approach, a library of peptides can be used as probes to screen for drugs. The peptides can be exposed to a receptor, and those probes that bind to the receptor can be identified. In one application, more than 10,000 protein spots were printed on a glass slide. The chip was used to identify protein-protein and protein-drug interactions (G. MacBeath and S. L. Schreiber, 2000, Printing Proteins as Microarrays for High-Throughput Function Determination, Science 189:1760–1763).
In more recent years, the demand for high-throughput and cost-effective analysis of complex mixtures has driven technology toward the fabrication of compact, high-density array devices. These arrays are fabricated using conventional techniques such as ink-jet printing, screen printing, photolithography, and photodeposition, in which the sensing chemistries are applied directly to the sensor surface. Typically, an array is fabricated by attaching a nucleic acid or peptide directly to a substrate. Multiple fabrication steps are commonly required that are labor intensive and subject to some degree of variability.
Given current fabrication schemes, the precise location of a probe on the surface of an array must be known prior to interrogating a sample. Therefore, fabrication of the arrays relies upon such techniques as printing or spotting of the probe onto the surface of the array, so that the addresses or locations of each probe is known prior to use of the array. Once the complexes are detected, the location of the complex is compared to the mapped surface of the array, and the identity of the target is determined.